Enhancing the cycling performance of sulfide-based all-solid-state lithium batteries via molecular weight-dependent fibrillation of PTFE binders

Abstract

Sulfide-based all-solid-state lithium batteries offer greater safety and higher energy density than lithium-ion batteries. An appropriate polymer binder for composite cathodes must be selected to ensure stable interfacial contact and minimize electrical resistance. Polytetrafluoroethylene (PTFE) binders, commonly used in solvent-free dry processes, undergo fibrillation under shear force to bind the cathode components. However, insufficient fibrillation and aggregation can compromise the mechanical and electrical integrity of the composite cathode, deteriorating cycling performance. In this study, we investigated the effect of PTFE molecular weight (MW) on the fibrillation behavior of the binder in composite cathodes. High-MW PTFE exhibited superior fibrillation and cohesion of the cathode components, enhanced mechanical properties, and reduced internal resistance. Consequently, the Li-In/Li6PS5Cl/LiNi0.82Co0.10Mn0.08O2 cell employing highly fibrillated PTFE achieved a high discharge capacity of 209.7 mAh g-1 (4.72 mAh cm-2) at 0.05 C and good capacity retention of 97.4 % after 300 cycles at 30 degrees C and a rate of 0.5 C.